Prediction models for the recipients’ ideal perioperative estimated glomerular filtration rates for predicting graft survival after adult living-donor kidney transplantation

Introduction The impact of the perioperative estimated glomerular filtration rate (eGFR) on graft survival in kidney transplant recipients is yet to be evaluated. In this study, we developed prediction models for the ideal perioperative eGFRs in recipients. Methods We evaluated the impact of perioperative predicted ideal and actual eGFRs on graft survival by including 1,174 consecutive adult patients who underwent living-donor kidney transplantation (LDKT) between January 2008 and December 2020. Prediction models for the ideal perioperative eGFR were developed for 676 recipients who were randomly assigned to the training and validation sets (ratio: 7:3). The prediction models for the ideal best eGFR within 3 weeks and those at 1, 2, and 3 weeks after LDKT in 474 recipients were developed using 10-fold validation and stepwise multiple regression model analyzes. The developed prediction models were validated in 202 recipients. Finally, the impact of perioperative predicted ideal eGFRs/actual eGFRs on graft survival was investigated using Fine–Gray regression analysis. Results The correlation coefficients of the predicted ideal best eGFR within 3 weeks and the predicted ideal eGFRs at 1, 2, and 3 weeks after LDKT were 0.651, 0.600, 0.598, and 0.617, respectively. Multivariate analyzes for graft loss demonstrated significant differences in the predicted ideal best eGFR/actual best eGFR within 3 weeks and the predicted ideal eGFRs/actual eGFRs at 1, 2, and 3 weeks after LDKT. Discussion The predicted ideal best eGFR/actual best eGFR within 3 weeks and the predicted ideal eGFRs/actual eGFRs at 1, 2, and 3 weeks after LDKT were independent prognostic factors for graft loss. Therefore, the perioperative predicted ideal eGFR/actual eGFR may be useful for predicting graft survival after adult LDKT.


Introduction
Donor and recipient characteristics, operative factors, postoperative complications, and immunosuppressive drugs may affect graft function after living-donor kidney transplantation (LDKT).Specifically, donor and recipient characteristics, including donor age, recipient sex, and donor estimated glomerular filtration rate (eGFR), graft pathological features, and anti-human leukocyte antigen (HLA) donor-specific antibodies (DSAs) affect postoperative graft function (1)(2)(3).Postoperative graft function is also affected by operative factors and postoperative complications, including laparoscopic nephrectomy, warm ischemia time, urological and vascular complications, and rejection (4)(5)(6)(7).Calcineurin inhibitors can cause nephrotoxicity and lead to a low eGFR (8,9).Furthermore, postoperative graft function is considered a good predictor of graft survival.Studies have investigated the impact of the eGFR on graft survival at 1 year after kidney transplantation (KT) (2,(10)(11)(12)(13)(14)(15)(16).However, the effect of the perioperative eGFR on graft survival in LDKT is yet to be investigated.Previously, perioperative graft function was stratified and evaluated based on slow or delayed graft function (17,18).Several studies have developed prediction models for recipients' eGFRs at 1-5 years after KT (19)(20)(21).However, to our knowledge, no study has reported the development of prediction models for ideal eGFRs during perioperative LDKT.Therefore, we investigated the impact of perioperative actual eGFRs on graft survival in adult LDKT.Additionally, we developed prediction models for recipients' ideal eGFRs during the perioperative period to investigate the impact of predicted ideal eGFRs on graft survival.

Study design
This single-center retrospective cohort study was approved by the Nagoya Daini Red Cross Hospital's Institutional Review Board (Aichi, Japan; approval number: 1504) and was conducted following the principles of the Declaration of Helsinki.The study included 1,174 consecutive adult patients who underwent LDKT between January 2008 and December 2020.First, the impacts of the actual best eGFR within 3 weeks after LDKT and actual eGFRs at 1, 2, and 3 weeks and at 1, 3, 6, and 12 months after LDKT on graft survival were investigated in 1174 recipients.Second, prediction models were developed for the ideal best eGFR within 3 weeks and ideal eGFRs at 1, 2, and 3 weeks after LDKT.We developed prediction models based on 676 ideal recipients selected from 1,174 recipients.Finally, the impact of the predicted ideal best eGFR/actual best eGFR within 3 weeks and the predicted ideal eGFRs/actual eGFRs at 1, 2, and 3 weeks after LDKT on graft survival was investigated in 1174 recipients.This study was reported following the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines.

Participants
This study included all consecutive recipients who underwent LDKT at our hospital between January 2008 and December 2020.The recipients were followed up until August 2021.Additionally, we excluded recipients with an immunosuppressive regimen using iscalimab in clinical trials (two recipients) (Figure 1).All donor and recipient data were retrospectively collected from the medical records and analyzed anonymously; therefore, the requirement for informed consent was waived by the Nagoya Daini Red Cross Hospital's Institutional Review Board (Aichi, Japan; approval number: 1504).

Living donors
Living donors were selected according to the guidelines for living kidney donors in Japan (22).The laterality of the kidney for donor nephrectomy was determined using the results of technetium-99 m diethylene triamine pentaacetic acid (Tc-99m DTPA).A difference in Tc-99m DTPA ≥10% between the right and left kidneys indicated a nephrectomy of the inferior side.In contrast, a discrepancy in Tc-99m DTPA of <10% indicated left nephrectomy.Furthermore, data on donor characteristics, surgical outcomes, and perioperative complications were collected and analyzed.

Recipients
LDKTs were performed following the Istanbul Declaration.The recipients stayed at the hospital for 3 weeks after LDKT.After discharge, postoperative recipient assessments were performed fortnightly for the first 3 months and subsequently monthly at our hospital and local hospitals.Protocol biopsies were performed at 1 h after reperfusion as a baseline, and at 1 month after KT.
Data on donor and recipient characteristics and operative outcomes, actual eGFR after LDKT, graft survival, and recipient mortality were collected.These data were used to analyze the impact of the actual best eGFR within 3 weeks after LDKT as well as actual eGFRs at 1, 2, and 3 weeks and at 1, 3, 6, and 12 months after LDKT on graft survival.Additionally, to develop the prediction models for the ideal best eGFR within 3 weeks and ideal eGFRs at 1, 2, and 3 weeks after LDKT, data on donor and recipient characteristics and operative outcomes; perioperative adverse events; best eGFR within 3 weeks after LDKT; and actual eGFRs at 1, 2, and 3 weeks after LDKT were collected and analyzed.Furthermore, prediction models were developed for recipients with ideal graft conditions within 1 month after LDKT.Recipients who received grafts from donors with intraoperative adverse events; those who received transplanted grafts with arterial reconstruction or ligation of the thin upper pole artery; and those who experienced perioperative adverse events, conversion of the immunosuppressive regimen, recurrence of nephritis, calcineurin inhibitor toxicity, and rejection within 1 month were excluded from the development of the prediction models for ideal eGFRs within 3 weeks.The detailed reasons for excluding 498 recipients from the development of the prediction models are presented in Supplementary Table S1.Data on donor and recipient characteristics, predicted ideal eGFR/actual eGFR, graft survival, and recipient mortality were collected to investigate the impact of the predicted ideal eGFR/actual eGFR on graft survival.

Statistical analysis
Statistical analyzes of donor and recipient characteristics were performed using the Kruskal-Wallis test and the chi-square or Fisher's exact test for continuous and categorical variables, respectively.An estimation equation model was constructed to predict the eGFR.The independent variables used in the estimation equation were initially tested for collinearity in advance, and factors with collinearity were excluded to prevent overfitting the model.Subsequently, estimation equations were constructed on the training set and confirmed using the validation set.The patients were randomly categorized into two groups in a 7:3 ratio, of whom 474 and 202 were assigned to the training and validation sets, respectively (Figure 2).
A linear regression prediction model was constructed using the eGFR as the dependent variable of the training set to establish an equation for estimating the eGFR.Subsequently, a stepwise method with 10-fold validation was used to limit the variables to be included in the model, and the estimation accuracy was evaluated.The R and R-squared values were used to estimate the accuracy.Finally, the constructed estimation equations were evaluated for their accuracy on the validation set.
A Fine-Gray competing risk regression model was used to determine the prognostic factors for graft loss.The proportional hazard assumption was confirmed using a log-log plot for the Fine-Gray competing risk regression model.No interaction effects between the variables were found in the models using the interaction items.Covariates with a p-value <0.05 in the univariate logistic regression analysis were used in the multivariate logistic regression analysis.Statistical significance was set at 0.05 (two-sided).All analyzes were performed using the Statistical Package for the Social Sciences (Version 24.0,IBM Japan Ltd., Tokyo, Japan) and R version 4.0.3(R Core Team [2020], Vienna, Austria).

Study population
Overall, 1,176 adult LDKTs were performed at our hospital during this study, of which two LDKTs were excluded, and the remaining 1,174 recipients were included.The 1,174 recipients were followed up between January 2008 and August 2021 (median observation period: 77.0 [interquartile range, 45.0-117.0]months) and were included in the final analysis.

Operative outcomes of the donor and recipients
The operative outcomes of the donors and recipients are presented in Table 2.In the donor operation, significant differences were observed in donor nephrectomy operation time (p = 0.020) and operation methods (p < 0.001).In the recipient operation, significant differences were observed in cold ischemia time (p < 0.001), delayed graft function (p < 0.001), and occurrence of arterial thrombosis (p = 0.001), lymphocele (p < 0.001), incisional hernia (p = 0.007), and severe pneumonia (p = 0.001).

Impact of actual eGFR on graft loss
The results of the univariate Fine-Gray competing risk regression model for graft loss are presented in Supplementary Table S2.Significant differences were observed in male recipient (p = 0.032); preformed DSA (p = 0.013); preoperative desensitization (preoperative rituximab administration or splenectomy, preoperative double-filtration plasmapheresis, plasmapheresis, or intravenous immunoglobulin, p = 0.028); actual eGFR at 6 months after LDKT (p = 0.003); actual eGFR at 12 months after LDKT (p < 0.001); and donor age (p = 0.048).Table 3 and Supplementary Tables S3A-H show the graft loss risk of the actual best eGFR within 3 weeks after LDKT and actual eGFRs at 1, 2, and 3 weeks and at 1, 3, 6, and 12 months after LDKT adjusted for male recipient, preformed DSA, preoperative desensitization, and donor age using the multivariate Fine-Gray competing risk regression model.Significant differences were observed in the actual eGFRs at 6 and 12 months after LDKT (p = 0.015, hazard ratio [HR]: 0.946, 95% confidence interval [CI]: 0.904-0.989,p < 0.001; HR: 0.937, 95% CI: 0.907-0.967).Flowchart of the development of the prediction models for ideal eGFRs using 10-fold validation.Overall, 676 ideal recipients were selected to develop the prediction models.The recipients were randomly categorized into two groups in a 7:3 ratio (474 and 202 recipients for the training and validation sets, respectively).In the 474 recipients, 10-fold validation and stepwise multiple regression model analyzes were used to develop prediction models for ideal eGFRs, while the developed prediction models were validated in 202 patients.eGFR, estimated glomerular filtration rate.

Development of eGFR prediction models
Details of the recipients who met the inclusion and exclusion criteria for developing prediction models are presented in Supplementary Tables S4, S5.For developing prediction models, recipients with conversion of the immunosuppressive regimen, recurrence of nephritis, calcineurin inhibitor toxicity, rejection, operative adverse events in donor and recipient operations, and arterial reconstruction or ligation of the thin upper pole artery were excluded, and those with these factors were not identified as recipients for prediction models.
The donor and recipient characteristics and operative outcomes for the training and validation sets are presented in Supplementary Tables S6, S7.Significant differences were identified in donor sex (p = 0.042) and preoperative flow cytometry T cell crossmatch (p = 0.033).Supplementary Table S8 presents the training set results using 10-fold cross-validation for the ideal best eGFR within 3 weeks after LDKT.Model 4 had the best R and R-squared values (0.646 and 0.418, respectively).The best prediction model for the ideal best eGFR within 3 weeks after LDKT is presented in Supplementary Table S9.Additionally, the R and R-squared values in the validation set were 0.651 and 0.423, respectively (Table 4).Supplementary Table S10 presents the training set results using 10-fold cross-validation for the predicted ideal eGFR at 1 week after LDKT.Model 7 had the best R and R-squared values (0.573 and 0.328, respectively).Supplementary Table S11 shows the best prediction model for the predicted ideal eGFR at 1 week after LDKT, and the R and R-squared values in the validation set were 0.600 and 0.360, respectively (Table 4).Supplementary Table S12 shows the training set results using 10-fold cross-validation for the predicted ideal eGFR at 2 weeks after LDKT.Model 7 had the best R and R-squared values (0.619 and 0.383, respectively).Furthermore, the best-estimated model for the predicted ideal eGFR at 2 weeks after LDKT is presented in Supplementary Table S13.The R and R-squared values in the validation set were 0.598 and 0.358, respectively (Table 4).Supplementary Table S14 presents the training set results using 10-fold cross-validation for the predicted ideal eGFR at 3 weeks after LDKT, and model 7 had the best R and R-squared values (0.693 and 0.480, respectively).The best-estimated model for the predicted ideal eGFR at 3 weeks after LDKT is presented in Supplementary Table S15.Furthermore, the R and R-squared values in the validation set were 0.617 and 0.380, respectively (Table 4).

Impact of predicted ideal and actual eGFRs on graft loss
Supplementary Figures S1A-D shows the association between the perioperative predicted ideal and actual eGFRs.

p-value
Hazard ratio 95% confidence interval

Lower limit Upper limit
Actual best eGFR within 3 weeks after transplantation (mL/min/  Supplementary Tables S17A-D, in addition to the significant differences in predicted ideal eGFRs/actual eGFRs, significant differences were observed in male recipient, preformed DSA, and donor age.

Discussion
This study suggests that the actual eGFRs at 6 and 12 months after LDKT could be an independent risk factor for graft loss, although the actual eGFR within 3 months after LDKT does not seem to be a risk factor.However, the predicted ideal best eGFR/actual best eGFR within 3 weeks after LDKT and the predicted ideal eGFRs/actual eGFRs at 1, 2, and 3 weeks after LDKT might be independent prognostic factors for graft loss.
In this work, as LDKTs were performed between Asian (Japanese) recipients and donors, the race composition differed from those reported previously, and the BMI values of the recipients and donors were lower than those reported in previous works from different countries (24-26).In Japan, LDKT is limited between relatives.This may have contributed to the higher rate of ABO-incompatible KTs (33.4%) found in this study than those reported in previous studies on LDKT, although the rate of preformed-DSA KTs (7.1%) was similar to those reported in previous studies on LDKT (27,28).The desensitization protocols for ABO-incompatible and preformed-DSA KTs were similar to those of previous reports, although those for preformed-DSA KT have not been established (28-30).However, the de novo DSA, rejection, graft loss, and death with functioning graft rates during the median observation period of 77.0 months were 11.0, 3.3, 6.2, and 3.6%, respectively.Interestingly, these results are similar to those of previous reports from other countries (31)(32)(33).In this study, the routine hospital stay at our institution after the transplantation was 3 weeks, which might be longer than that in other countries (34,35).This might have facilitated a more in-depth investigation of post-LDKT graft function.
The eGFR at 1 year after KT could be a prognostic factor for graft loss (2,(10)(11)(12)(13)(14)(15)(16)(17).However, no studies to date have investigated the impact of eGFR within 1 year of KT.This study is the first to examine the effects of actual eGFRs within 1 year on graft loss.Using multivariate Fine-Gray competing model analysis, actual eGFRs at 6 and 12 months after LDKT, preformed DSA, and male recipient were shown to be independent prognostic factors for graft loss.In previous studies, the graft survival of recipients with preformed DSAs was worse than that of those without because of antibody-mediated rejection (AMR).However, desensitization was performed to prevent acute AMR (28, 29,31).Although many clinical studies on desensitization using intravenous immunoglobulin, rituximab, plasmapheresis, and imlifidase have been conducted to improve the graft survival of recipients with preformed DSAs, no desensitization regimen for preformed DSAs has been established (36)(37)(38)(39).Here, the recipients with preformed DSAs were desensitized using rituximab, plasmapheresis, and intravenous immunoglobulin administration.However, these desensitization procedures were ineffective in improving graft survival.Consistent with previous studies, male recipient was also found to be an independent prognostic factor for graft loss (40,41).This study is novel because it investigated the impact of the actual eGFRs on graft loss within 1 year after LDKT.Moreover, no studies have investigated the impact of the actual eGFRs at 1, 2, and 3 weeks and 1, 3, and 6 months after LDKT on graft survival (2,(10)(11)(12)(13)(14)(15).Therefore, this study revealed that actual eGFRs within 3 months after LDKT could not be an independent prognostic factor for graft loss.
Notably, the prediction models for ideal eGFRs at 1, 2, and 3 weeks after LDKT and the ideal best eGFR within 3 weeks were developed using 10-fold cross-validation and stepwise multiple regression model analysis.Ideal KTs were selected by excluding problematic donors and recipients during the perioperative period.Finally, data from 676 recipients were used to develop prediction models for ideal eGFRs during this period.This study is novel because no studies to date have investigated prediction models for ideal eGFRs during the perioperative period.During the development of the prediction models, the trough levels of tacrolimus and extended-release tacrolimus were separately presented, as they were found to be significantly different when the same dose was administered in a previous study (42).
Overfitting of the model was prevented using 10-fold crossvalidation (43,44).The predicted ideal best eGFR/actual best eGFR within 3 weeks after LDKT and predicted ideal eGFRs/actual eGFRs at 1, 2, and 3 weeks after LDKT were obtained in 1174 recipients to investigate the impact of ideal eGFRs/actual eGFRs on graft loss.In the multivariate Fine-Gray competing model analysis, covariates that were independent prognostic factors in the univariate Fine-Gray competing model analysis were used as follows: male recipient; preformed DSA; preoperative desensitization; donor age; predicted best eGFR/actual best eGFR within 3 weeks after LDKT; and predicted ideal eGFRs/actual eGFRs at 1, 2, and 3 weeks after LDKT.In the multivariate Fine-Gray competing model analysis, in addition to the predicted ideal best eGFR/actual best eGFR within 3 weeks after LDKT and predicted ideal eGFRs/actual eGFRs at 1, 2, and 3 weeks after LDKT, male recipient, preformed DSA, and donor age were independent prognostic factors for graft loss (3,28,29,31,40,41).In this analysis, male recipient and preformed DSA were the prognostic factors for graft loss, similar to those indicated by the multivariate analyzes for the impact of actual eGFRs on graft loss.Additionally, donor age was found to be an independent prognostic factor for graft

p-value
Hazard ratio 95% confidence interval loss.This result is consistent with those of previous studies indicating that graft loss may occur more frequently when the graft is transplanted from elderly donors owing to donor age-related graft nephrosclerosis (3,41,45).Furthermore, the graft loss risk of the predicted ideal eGFRs/actual eGFRs adjusted with the multivariate Fine-Gray competing model analysis using male recipient, preformed DSA, and donor age as factors was significant.These results show that the graft loss risk increases as the predicted ideal eGFR/actual eGFR increases.Moreover, this implies that when recipients receive actual eGFRs that are lower than those of the predicted ideal eGFR, the graft survival may be worse than that of recipients who obtained better eGFRs than the predicted ideal eGFR.Although actual eGFRs at 1, 2, and 3 weeks after LDKT were not significant predictors for graft loss, those at 6 and 12 months after LDKT were significant predictors.This implies that we cannot predict graft loss based on the actual eGFRs at 1, 2, and 3 weeks after KT.The P-values in the multivariate Fine-Gray competing model analysis for graft loss, adjusted for male recipient, preformed DSA, preoperative desensitization, and donor age, decreased as the time after KT passed.This may imply that the widening disparities of the actual eGFR after KT between the graft loss and non-graft loss groups did not contribute to graft loss prediction until 6 months after KT.However, it may be useful to reveal the predictor for graft loss earlier and implement measures based on the results.Therefore, the predicted ideal eGFR/actual eGFR was successfully developed to make the eGFRs at 1, 2, and 3 weeks more useful predictors for graft loss.This finding enabled the detection of slightly widening disparities of eGFR after KT between the graft loss and non-graft loss groups, which could not be detected using the actual eGFR after KT.Many factors might prevent recipients from obtaining an ideal eGFR during the perioperative period, including rejection, delayed graft function, and operative complications (7,46,47).However, the period of 3 weeks after LDKT is early to optimize immunosuppression, treat comorbidities, and detect and treat surgical complications, including graft vascular stenosis and urinary tract obstruction.Therefore, to obtain the ideal eGFR, preventing rejection, delayed graft function, and intraoperative surgical complications, which may negatively affect graft function within 3 weeks after LDKT, might be crucial.These results are novel because long-term graft survival can be predicted using prediction models for perioperative ideal eGFRs.Accordingly, this study demonstrated the importance of obtaining an ideal eGFR during the perioperative period.
Furthermore, considering the recent advancements in artificial intelligence technology, the development of tools for predicting eGFR after KT using data from large-scale multicenter studies is expected.Therefore, this study's results, which suggest the potential utility of a predictive tool for the ideal eGFR rather than relying solely on the actual eGFR, can lead to the advancement of innovative studies in the field of KT.
The retrospective design of the study and the fact that it was conducted in a single institution to examine the impact of predicted eGFRs on graft survival were limitations of this work.Therefore, a prospective multicenter randomized study focusing on the effects of predicted ideal eGFRs/actual eGFRs on graft survival should be conducted to verify the results and elucidate the causes of failure to obtain ideal eGFRs.
In conclusion, the predicted ideal eGFRs/actual eGFRs at 1, 2, and 3 weeks after LDKT and the predicted ideal best eGFR/actual best eGFR within 3 weeks may forecast graft survival after adult LDKT.Therefore, obtaining an ideal perioperative eGFR is crucial for improving long-term graft survival.

TABLE 1
Donor and recipient characteristics.Preoperative flow cytometry B cell crossmatch after desensitization for preformed DSA became false positive when rituximab was administered.ICFA classes I and II were examined for recipients who received rituximab.The bold font indicates statistically significant results.

TABLE 2
Donor and recipient operative outcomes.

TABLE 3
Multivariate Fine-Gray competing model analysis for graft loss adjusted for male recipient, preformed DSA, preoperative desensitization, and donor age.
, donor-specific antibody; eGFR, estimated glomerular filtration rate.The bold font indicates statistically significant results. DSA

TABLE 4
Coefficients in the validation set.

TABLE 5
Multivariate Fine-Gray competing model analysis for graft loss adjusted for male recipient, preformed DSA, preoperative desensitization, and donor age.